1. Field of the Invention
The present invention relates to a process for purifying crude hydroquinone containing impurities by subliming the crude hydroquinone with an apparatus having a stirred and fluidized bed and then collecting only the hydroquinone which has been fractionally solidified in a condenser.
2. Description of the Prior Art
In general, the hydroquinone used in photo-chemical industries requires high purity. Crude hydroquinone prepared according to a process as described in U.S. Pat. No. 2,715,646 and British Patent No. 641,250 for the liquid phase oxidation of para-diisopropyl-benzene contains about 10% of inorganic salts as well as traces of several tens of different kind of impurities, and it is known that these trace impurities cause some coloration which is harmful to the quality of the product and that some impurities additionally deleteriously affect photographic characteristics.
When attempts are made to completely remove these trace impurities using an extraction process, an adsorption process or the like separation process, such processes are too expensive, and therefore they are unsuitable industrially. On the other hand, a separation using a distillation also is unsuitable for the purification of hydroquinone in that the hydroquinone is easily oxidized in the distillation process and that hydroquinone reacts with the existing trace impurities therein and polymerizes or changes into other substances.